• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.366.2-366
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• 2002

Unsteady flow characteristics and associated blade tonal noise of a cross-flow fan are predicted by a computational method. The incompressible Wavier-Stokes equations are time-accurately solved for obtaining the pressure fluctuations between the rotating blades and the stabilizer, and sound pressure is predicted using Curie's equation. The computed fan performance is favorably compared with experimental data, and also indicates that the performance is not significantly altered by the random pitch effect at ø〉0.4. (omitted)

• 한국분무공학회지
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• 제24권3호
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• pp.105-113
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• 2019

In this paper, a study of Urea-SCR System for Dosing Injector for responding to enhanced environmental regulations has been conducted. There is a limit to the experimental approach due to the structural characteristics of the injector. In order to overcome this problem, The analysis was performed assuming unsteady turbulent flow through computational fluid analysis and the internal flow characteristics of the injector were analyzed. By changing the nozzle shape of the injector, the performance factors of the swirl injector by shape were selected and compared. The design parameters were modified by changing the diameter of the nozzle at a constant ratio compared to the base model. Swirl coefficient, outlet mass flow, and sac volume were selected as performance parameters of the injector. The Conv. model to which the taper was applied showed the dominance in mass flow rate, discharge coefficient and swirl because of the smooth fluid flow by shape. Swirl coefficient, outlet mass flow, and sac volume were selected as performance parameters of the injector. As a result of the comparison coefficient derivation with those performance parameters for comparing the performance of the model-specific injector, the Conv-140 model with the nozzle diameter expanded by 140% showed the best value of the comparison coefficient.

• 한국항공우주학회지
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• 제39권7호
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• pp.634-642
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• 2011

비행조종작동기 제어용 파일럿 밸브의 내부 유동 및 응답 특성을 분석하기 위해 캐비테이션 모델과 격자 이동 기법을 사용하여 정상/비정상 유동의 수치 해석을 수행하였다. 작동 온도와 시간에 따른 밸브 내부 유동을 분석한 결과, 일정 온도 이상에서 밸브 특성이 안정되는 현상을 발견하였고 캐비테이션이 밸브 성능에 미치는 영향성을 파악하였다. 밸브 내부 압력과 응답 특성을 분석하였으며 비정상 유동이 발달하여 정상 유동 특성과 일치하는 것을 확인하였다.

• 대한기계학회논문집
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• 제18권11호
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• pp.3046-3056
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• 1994

To design and develop a turbocharged engine, it needs that many studies must be preceded about the characteristics of engine performance and thermal flow. To accomplish this purpose, turbocharger was equipped to 1.3 liter naturally aspirated gasoline engine. The temperature probe of plate type was designed and it was installed into the combustion chamber wall to measure unsteady temperature. The unsteady heat flux at combustion chamber wall was evaluated using one dimensional unsteady conduction equation with the wall temperature and temperature gradient.

• 한국안전학회지
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• 제25권1호
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• pp.9-16
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• 2010

Flame structure of diffusion flame interacting with a single vortex was investigated with direct numerical simulation (DNS). A well-known counterflow diffusion flame was used as an initial flat flame and single vortices were made by issuing a high-velocity jet abruptly in fuel- and air-side. The variations in the maximum concentration of major species (CO and $CO_2$) and NOx (NO and $NO_2$) with the stoichiometric scalar dissipation rate were investigated. Unsteady effects in the species concentration variation of the flame interacting with a vortex were identified by comparing with that of steady flame. $NO_2$ formation characteristics of the flame interacting with a vortex were well understood by investigating the $HO_2$ formation. To enhance the prediction performance in the fire simulation, current turbulent combustion modelings are needed to be modified by adopting the unsteady effects in the species concentrations of diffusion flame interacting with a vortex.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문초록집
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• pp.334.1-334
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• 2002

In this study, a cross-flow fan system used in indoor unit of the split-type air conditioner is analyzed by computational simulation. A commercial CFD code - Fluent - is used to calculate the performance and its unsteady flow characteristics. The unsteady incompressible Wavier-Stokes equations are solved using a sliding mesh technique on the interface between rotating fan region and the outside. The acoustic pressure is calculated by using Ffowcs-Williams and Hawkings equation. (omitted)

• 한국유체기계학회 논문집
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• 제5권3호
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• pp.15-24
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• 2002

This paper presents an experimental study on the unsteady flow phenomena such as leakage flow and rotating stall which have influences on the performance and stability of an axial flow fan. For this study, unsteady pressure were measured using high frequency pressure transducers mounted on the easing wall of rotor passage and analyzed by Double Phase-Locked Averaging Technique. As the flow rate was reduced to near stall point, the pressure difference between the pressure and the suction side of the blade was increased especially new the leading edge and the lowest pressure zone of suction side was gradually developed. From the result of unsteady pressure field on the casing wall, one period of rotating stall was divided into three zones and the flow characteristics on each zone were described in detail.

• 한국유체기계학회 논문집
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• 제5권3호
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• pp.46-53
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• 2002

This paper reports an experimental investigation on a centrifugal compressor with the adjustable inlet guide vane. The compression system is composed of a radial impeller, a vaneless diffuser, and an IGV. The results have shown that surge line on the performance map is affected by the amount of prewhirl and the prewhirl has an effect on transient region between rotating stall and surge. The surge lines have been shifted toward the lower flow region with the increased positive prewhirl and the higher flow region with the increased negative prewhirl. During the unsteady performance test, it was also found that the transient region was reduced with the increased negative prewhirl, and weak signals of rotating stall were detected just before surge as the positive prewhirl was increased.

• 한국추진공학회지
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• 제22권3호
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• pp.28-39
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• 2018

본 연구에서는 추력조절용 핀틀 노즐의 길이비에 따른 정상상태와 비정상상태 특성을 파악하기 위해 수치해석을 수행하였다. 노즐과 핀틀의 영역은 분리하여 격자를 생성하고 중첩격자기법을 사용하였다. 핀틀 형상은 길이비에 따라 5가지로 선택하였고, 정상상태 해석결과 핀틀의 길이가 길수록 추력과 추력계수가 높게 나타났다. 비정상상태 해석의 경우 핀틀의 속도에 따라서 연소실 압력 경향이 달라지며 추력과 유동구조에 영향을 미친다. 노즐 출구에서의 추력은 노즐목 단면적 변화에 빠른 응답특성을 보이며, 추력과 추력계수 등 성능 주요 인자들의 예측시 핀틀의 구동 속도와 핀틀 거동에 의한 연소실 압력파의 전달속도를 고려해야 한다.

• 한국유체기계학회 논문집
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• 제12권1호
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• pp.22-27
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• 2009

The important problems that arise in the design and performance of the axial flow turbine are the prediction and control of secondary flows. Some progresses have been made on understanding flow conditions that occur when the inlet endwall boundary layer separates at the point in the endwall and rolls up into the horseshoe vortex. And the flows though an axial turbine tend to be extremely complex due to its inherent unsteady and viscous phenomena. The passing wakes generated from the trailing edge of the stator make an interaction with the rotor. Unsteady flow should be considered rotor/stator interactions. The main purpose of this research is control of secondary flow and improvement efficiency in turbine by leading edge modification in unsteady state. When the wake from the stator ran into the modified leading edge of the rotor, the leading edge generated the weak pressure fluctuation by complex passage flows. In conclusion, leading edge modification(bulb2) results in the reduced total pressure loss in the flow field.